In a Long Term Evolution (LTE) system and earlier wireless communication systems, typically only one carrier is configured for a cell to transmit data. FIG. 1 illustrates a schematic diagram of a carrier in the LET system in which a bandwidth of the carrier is up to 200 MHz, where t represents the time domain and f represents the frequency domain.
Along with continuous evolution of the LTE system, in a Long Term Evolution-Advanced (LTE-A) system, there are required peak rates of the system, typically up to 1 Gbps in the downlink and 500 Mbps in the uplink, as improved significantly over the LTE system. Apparently the required peak rates of the LTE-A system can not be reached with only one carrier with a bandwidth up to 20 MHz. Thus in order to support a higher bandwidth of the system, it is necessary in the LTE-A system to extend a bandwidth available to a User Equipment (UE), and in view of this, Carrier Aggregation (CA) technology has been introduced where a plurality of consecutive or inconsecutive carriers served by the same base station (eNB) are aggregated together to serve the UE concurrently for providing a desirable rate, where the carriers aggregated together are referred to Component Carriers (CCs).
In the LTE-A system with the carrier aggregation, each cell can be a component carrier, and cells (or component carriers) served by different eNBs can not be aggregated. In order to ensure the UE in the LTE system to be able to operate over each of the aggregated carriers, each of the carriers has a bandwidth of no more than 20 MHz. FIG. 2 illustrates a schematic diagram of carrier aggregation in the LTE-A system, in which four carriers each with a bandwidth of 20 MHz are aggregated, where t represents the time domain and f represents the frequency domain. In the schematic diagram of carrier aggregation illustrated in FIG. 2, in the LTE-A system, four carriers, which can be aggregated, are served by the base station so that the base station can transmit data with the UE concurrently over the four carriers to thereby significantly extend the bandwidth of the system for an improved throughput of the system.
In the LTE system, a radio frame is 10 ms and a sub-frame is 1 ms in both the Frequency Division Duplex (FDD) mode and the Time Division Duplex (TDD) mode. Seven TDD uplink and downlink sub-frame configurations are defined for each TDD radio frame, particularly as depicted in Table 1 below, where D represents a downlink (DL) sub-frame, U represents an uplink (UL) sub-frame, and S represents a special sub-frame in the TDD system.
TABLE 1(TDD uplink and downlink sub-frame configurations)Uplink andSub-frame indexdownlink configuration01234567890DSUUUDSUUU1DSUUDDSUUD2DSUDDDSUDD3DSUUUDDDDD4DSUUDDDDDD5DSUDDDDDDD6DSUUUDSUUD
In the LTE system, a Hybrid Automatic Repeat ReQuest (HARQ) timing of a Physical Downlink Shared Channel (PDSCH) is further specified in details. Particularly in the LTE FDD system, the UE receives downlink data in the downlink sub-frame n−4 and feeds back, in the uplink sub-frame n, response information of whether the data in the downlink sub-frame needs to be retransmitted, the response information generally includes Acknowledge (ACK) or Negative-Acknowledge (NACK). With carrier aggregation, ACK/NACK information corresponding to a plurality of downlink carriers in the sub-frame n−4 will be fed back in the uplink sub-frame n concurrently. In the LTE TDD system, the UE may feed back, ACK/NACK information corresponding to a plurality of downlink sub-frames, in the same uplink sub-frame, that is, the UE detects transmission of a Physical Downlink Shared Channel (PDSCH), or a Physical Downlink Control Channel (PDCCH) indicating downlink semi-persistent scheduling to be released, in the downlink sub-frame n−k and feeds back corresponding ACK/NACK information in the uplink sub-frame n, where k∈K, and values in the set K depend upon an uplink and downlink sub-frame configuration of the TDD system and a particular sub-frame index, as depicted in Table 2. Particularly for a special sub-frame with a normal Cyclic Prefix (CP) configured with 0 and 5 and for a special sub-frame with an extended CP configured with 0 and 4, and there is no ACK/NACK feedback for the special sub-frame, that is, the UE will not feed back ACK/NACK for the special sub-frame.
TABLE 2related TDD downlink K values: {k0, k1, . . . kM−1}Uplink anddownlinkSub-frame indexconfiguration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7, 4, 6——3——7, 6, 116, 55, 4—————4——12, 8, 7, 116, 5, 4, 7——————5——13, 12, 9, 8, 7, 5, 4, 11, 6———————6——775——77—
In a practical application, a plurality of radio frames are arranged in order, that is, if the last sub-frame in the radio frame a is k, then the first sub-frame in the radio frame a+1 is k+1, and Table 2, which takes only one radio frame as an example, depicts values of K corresponding to respective uplink sub-frames, where n−k<0 indicates a downlink sub-frame in a preceding radio frame.
In the LTE system, a solution to transmission of ACK/NACK information generally includes: transmitting ACK/NACK information over a Physical Uplink Control Channel (PUCCH). That is, the base station pre-configures the UE with a carrier over which the PUCCH is transmitted (referred to a PUCCH transmission carrier), and correspondingly the UE feeds back the ACK/NACK information over the PUCCH transmission carrier configured by the base station.
With the solution to transmission of ACK/NACK information above, the UE may move outside a coverage area of the PUCCH transmission carrier while the UE is moving due to the mobility of the UE, so that it is necessary for the base station to reconfigure the UE, however, the UE may not communicate normally on one hand in the reconfiguration procedure, and there will be an increase in signaling overhead due to reconfiguration operations.